Food Chains & Food Webs

D. Crowley, 2008

Key terms

Producer - utilise the sun’s energy to produce their own food, e.g. plants and algae

Consumer - organisms that eat other organisms for their energy supply. These can be primary consumers which eat the producers; secondary consumers which eat the primary consumers; or tertiary consumers which eat the secondary consumers etc…

Herbivore - an organism that eats other producers (plants), e.g. cow

Omnivore - an organism that eats both producers and consumers, e.g. human

means ‘eaten by’

Top predator – the organism at the top of the food chain: it isn’t eaten by other organisms

Carnivore - an organism that eats other consumers, e.g. lion

Food Chains & Food Webs

To understand food chains and food webs, and the transfer of energy within these

Carnivore, Herbivore or Omnivore

Carnivore

Herbivore

Omnivore

Carnivore

Herbivore

Herbivore

Omnivore

Omnivore

Carnivore

Food Chains

What is a food chain?

A food chain shows what is eaten by what – each arrow means ‘eaten by’

E.g. rabbit fox means the rabbit is eaten by the fox

Food Chains

What is the food chain in the following habitat: -

Food Chains

• This food chain shows a leaf is eaten by a caterpillar, which is eaten by a bird, which is eaten by a cat

• Why do the organisms eat one another?

• Energy is transferred from one organism to another, in the direction of the arrow

Producer 1° Consumer(Herbivore)

2° Consumer(Carnivore)

3° Consumer(Carnivore)

Energy

• Food chains are never very long (usually only 4/5 stages at most) – why is this?

• Remember the arrow shows the energy being transferred from

one organism to the next - between each step energy is ‘lost’ in a variety of ways, including: -– Growth of the organism– Reproductive costs– Lost through waste products (poo)– Lost through heat

• This is why food chains are never that long - as lots of energy is ‘lost’ from one stage to the next

Food Chains

• Your task is to make 3 food chains consisting of at least 3/4 organisms in each – e.g. leaf caterpillar bird cat

• For each food chain draw out your animals, adding the key words: producer, consumer (1°; 2°; 3°) and if you can: herbivore, carnivore or omnivore

• Once you have done this complete a food chain for your favourite celebrity / sports person / musician / actor etc… with a paragraph underneath explaining how they live based on this food chain

Food Webs• In most habitats organisms normally eat / are eaten by more than

one other organism• To represent this we use food webs (like food chains but they

interlink with one another), e.g. a pond

Here the producers are the pondweed and the microscopic algae

Mayfly nymphs eat the pondweed and microscopic algae, and freshwater shrimp eat the microscopic algae

Dragonfly nymphs and brown trout eat the mayfly nymphs and freshwater shrimp

Brown trout also eat the dragonfly nymph!

Food Webs

blue tit

chiffchaff

aphid

moth larva

vole

stoat

owl

spider

ladybird

plants

Food Webs

• You have 5 minutes to have an answer to every question (you do not need to write your answers down): -

1. Name the producer2. Name 2 herbivores3. Name 2 top carnivores4. How many 2° consumers are

there?5. Which food chains include a

moth larva

1. Plants2. Vole; moth larva; aphid3. Stoat; owl4. 5 - stoat; spider; ladybird; blue tit;

owl5. Blue and orange food chain

B: peach tree    peach-potato aphid    swallow   sparrowhawk

C: potato plant    beetle   mole   badger

E: peach tree   peach-potato aphid    spider   blue tit   cat

F: lettuce   rabbit    fox

G: lettuce peach-potato aphid hoverfly lava blue tit sparrowhawk

EXTENSION

Collect and cut up these food chains and use them to

create a food web. Remember only stick them down

when you are happy with the

position of all the animals

Balance

Populations in a food chain are dependent upon one another – there is a balance between the producers and consumers in the food chain

For example if there are lots of giraffes they will eat a large quantity of the trees and shrubs until there may be insufficient amounts to support them. If this is the case many will begin to starve and die.

Fewer giraffes means less food for lions, which will eventually see a population decrease.

Less giraffes will allow more shrubs and tress to survive, so the giraffe population recovers, leading to the lion population recovering, until the process repeats itself…

Food Examples

• Complete the food chains and food webs worksheet

Food Examples